Conventionally, pressure vessels for receiving high pressure gas are known to include a partition wall dividing the inside thereof into two chambers. For example, Patent Document 1 discloses a pressure vessel having a vessel main body for receiving high pressure gas and a partition wall formed in the vessel main body so as to divide the inside thereof in half into a first chamber and a second chamber. The vessel main body includes a first side cylindrical wall and a second side cylindrical wall which are joined together with the partition wall being sandwiched therebetween. The vessel main body has an elongated shape in one direction. The partition wall is formed in the shape of a flat plate extending along the direction parallel to the longitudinal direction of the vessel main body. An upper end of the partition wall is connected to an upper part of the vessel main body, and a lower end of the partition wall is connected to a lower part of the vessel main body.
When the high pressure gas is received in the respective chambers of this pressure vessel, a load of the first side cylindrical wall and the second side cylindrical wall to expand outwardly is applied thereon. At this time, stress concentration occurs in connection parts of each cylindrical wall and the partition wall. Therefore, the upper end and the lower end of the partition wall are each formed with a widened portion having a thickness larger than that of other parts of the partition wall.
However, it cannot be said that the pressure vessel described in Patent Document 1 can sufficiently suppress the occurrence of stress concentration on the pressure vessel. That is, when the high pressure gas is received in the respective chambers of this pressure vessel, the respective cylindrical walls are deformed to expand outwardly, and therefore stress concentration occurs in the boundaries of thickness-direction ends of the widened portions and the respective cylindrical walls. (Hereinafter referred to as “a first problem”.)
In addition, since the partition wall is connected to the upper part and the lower part of the vessel main body, the partition wall is pulled to the vertical direction (the direction orthogonal to each of the longitudinal direction and the thickness direction of the partition wall) by the upper part and the lower part of the vessel main body to expand outwardly when the load is applied on the respective cylindrical walls. Thereby, a tensile load in the vertical direction acts on the partition wall. It should be noted that substantially equal pressure from both the chambers adjacent to each other in the thickness direction is applied on the partition wall and therefore a bending moment hardly acts on the partition wall even if the high pressure gas is received in the respective chambers.
In general, the pressure vessels are required to secure a pressure resistant breaking strength larger than a predetermined value, as major design requirements on the strength. On the other hand, there is a need for reducing the weight of the pressure vessel as much as possible while satisfying the required design requirements. However, in the pressure vessel described in Patent Document 1, the partition wall requires a large enough thickness to withstand the tensile load, so that it is difficult to reduce the weight of the pressure vessel. (Hereinafter referred to as “a second problem”.)